An ATM (Automatic Teller Machine) which receives/discharges banknotes at a banking institution such as a bank has therein a thickness detecting apparatus which detects the thickness of a bank note to screen the bank note. As it is known, an ATM of this kind is becoming smaller and smaller year after year and, accordingly, reduction in the size of the thickness detecting apparatus is in increasing demand.
FIG. 7(a) is a side view showing the configuration of a conventional thickness detecting apparatus 10. The thickness detecting apparatus 10 shown in the drawing is an apparatus which is disposed above a carrying path M and detects thickness t1 and t2 of sheets P of paper carried in the direction X of the carrying path M. In the thickness detecting apparatus 10, a casing 11 houses the components. A board 12 is attached to attachment bases 11b and 11c of the casing 11. A supporting roller 13 is disposed rotatably on the right side of an opening 11a of the casing 11 to support a detection roller 15 via an arm 14.
The detection roller 15 is disposed in the opening 11a so that a part of it is projected toward the carrying path M side, and rotatably attached to the tip of the arm 14. The detection roller 15 is rotated in a state where it is in contact with the sheet P of paper, and displaced in the direction Z in accordance with the thickness of the sheet P of paper. That is, the detection roller 15 is a roller which detects the thickness of the sheet P of paper as a displacement amount.
A potentiometer 16 is disposed on the left side of the opening 11a and outputs a voltage according to the rotation amount of a rotary shaft 16a. A linking member 17 links the detection roller 15 and the potentiometer 16. Specifically, one end 17a of the linking member 17 is coupled to a shaft 15a of the detection roller 15, and the other end 17b of the linking member 17 is coupled to the rotary shaft 16a of the potentiometer 16. Specifically, the displacement amount in the direction Z of the detection roller 15 is transmitted to the rotary shaft 16a of the potentiometer 16 via the linking member 17 and detected as the rotation amount (voltage) of the rotary shaft 16a by the potentiometer 16.
In the configuration, when the sheet P of paper is carried in the direction X, the detection roller 15 is rotated in a state where it is in contact with the surface of the sheet P of paper and is displaced in the direction Z in accordance with the thickness t1 (or thickness t2) of the sheet P of paper by using the supporting roller 13 as a rotary shaft. Interlockingly with the displacement of the detection roller 15, the rotary shaft 16a of the potentiometer 16 rotates in a direction A. The rotation amount of the rotary shaft 16a corresponds to the thickness t1 (or thickness t2) of the sheet P of paper. A voltage according to the rotation amount of the rotary shaft 16a is output from the potentiometer 16 and is converted to the thickness t1 (or thickness t2) of the sheet P of paper by a not-illustrated detection circuit.
FIG. 7(b) is a side view showing the configuration of a conventional thickness detecting apparatus 20. The thickness detecting apparatus 20 shown in the diagram is another configuration as an example and is disposed above the carrying path M. In the thickness detecting apparatus 20, a casing 21 houses the components. Aboard 22 is attached to an attachment bases 21b and 21c of the casing 21. A supporting roller 23 is rotatably disposed near an opening 21a of the casing 21 to support a detection roller 25 via an arm 24.
The detection roller 25 is disposed in the opening 21a so that a part of it is projected toward the carrying path M side and is rotatably attached to the tip of the arm 24. The detection roller 25 is rotated in a state where it is in contact with the sheet P of paper and is displaced in the direction Z in accordance with the thickness of the sheet P of paper. That is, the detection roller 25 is a roller which detects the thickness of the sheet P of paper as a displacement amount.
A member 26 is a plate member having a rectangular shape and is provided vertically on a shaft 25a of the detection roller 25. A potentiometer 27 has the same configuration as that of the potentiometer 16 (refer to FIG. 7(a)) and is disposed below the board 22. The potentiometer 27 outputs a voltage according to the rotation amount of a rotary shaft 27a. 
A rotating member 28 is a plate member having a substantially U-letter shape and is attached to the rotary shaft 27a. A linking member 29 indirectly links the detection roller 25 and the potentiometer 27 via the member 26 and the rotating member 28. One end 29a of the linking member 29 is coupled to a fulcrum member S, and the linking member 29 is provided rotatably in the direction B by using the fulcrum member S as a fulcrum. The other end 29b of the linking member 29 is in contact with a contact portion 28a of the rotating member 28, and a coupling portion 29c is coupled to a coupling portion 26a of the member 26.
To be specific, the displacement amount in the direction Z of the detection roller 25 is transmitted to the rotary shaft 27a of the potentiometer 27 via the member 26, the linking member 29, and the rotating member 28, and is detected as a rotation amount (voltage) of the rotary shaft 27a by the potentiometer 27.
In the configuration, when the sheet P of paper is carried in the direction X, the detection roller 25 is rotated in a state where it is in contact with the surface of the sheet P of paper, and is displaced in the direction Z in accordance with the thickness t1 (or thickness t2) of the sheet P of paper by using the supporting roller 23 as a rotary shaft. Interlockingly with the displacement of the detection roller 25, the rotary shaft 27a of the potentiometer 27 rotates in the direction A. The rotation amount of the rotary shaft 27a corresponds to the thickness t1 (or thickness t2) of the sheet P of paper. A voltage corresponding to the rotation amount of the rotary shaft 27a is output from the potentiometer 27 and converted into the thickness t1 (or thickness t2) of the sheet P of paper by a not-illustrated detection circuit.
Conventionally, other than the configuration using the potentiometer, there is also a thickness detecting apparatus 30 having the configuration shown in FIG. 8. FIG. 8 is a side view showing the configuration of the conventional thickness detecting apparatus 30. The thickness detecting apparatus 30 shown in FIG. 30 is disposed above the carrying path M. In the thickness detecting apparatus 30, a casing 31 houses the components.
A board 32 is disposed in parallel with the carrying path M so as to be fixedly supported by both faces of the casing 31. A coil 33 is attached to an attachment hole 32a in the board 32 so as to penetrate the attachment hole 32a. The lower part of the coil 33 is projected from the back side of the board 32 towards an opening 31a. 
The thickness detecting circuit 34 is a circuit which electrically detects the thickness of the sheet P of paper and includes an oscillation circuit 35, a resistor 36, a capacitor 37, a detection circuit 38, and an amplifying circuit 39. The oscillation circuit 35 generates a high frequency signal. The oscillation circuit 35 is grounded via the resistor 36 and capacitor 37.
The detection circuit 38 is a circuit which detects a direct current signal according to the amplitude of the high frequency signal from the oscillation circuit 35. The direct current signal is a signal proportional to the distance (thickness of the sheet P of paper) between a detection roller 43 to be described herein later and the coil 33. The amplifying circuit 39 amplifies the direct current signal input from the detection circuit 38. An output signal of the amplifying circuit 39 corresponds to the thickness of the sheet P of paper as a result of the thickness detection. A cable 40 connects the coil 33 and the capacitor 37 in the thickness detection circuit 34.
The detection roller 43 is disposed below the coil 33 and near the opening 31a of the casing 31 and is rotatably supported by a supporting roller 41 via a shaft 43a and an arm 42. The detection roller 43 is a conductor. A part of the detection roller 43 is projected from the opening 31a toward the carrying path M side. The detection roller 43 is rotated in a state where it is in contact with the sheet P of paper and is displaced in the direction Z in accordance with the thickness of the sheet P of paper. That is, the detection roller 43 is a roller which detects the thickness of the sheet P of paper as a displacement amount.
In the configuration, when the oscillation circuit 35 is driven, a high frequency signal is supplied from the oscillation circuit 35 to the coil 33 via the resistor 36, capacitor 37, and the cable 40. Consequently, a high frequency current is passed to the coil 33 and a high-frequency field is generated around the coil 33.
When the sheet P of paper is carried in the direction X in such a state, the detection roller 43 is rotated in a state where it is in contact with the surface of the sheet P of paper and is displaced in the direction Z in accordance with the thickness t1 (or thickness t2) of the sheet P of paper by using the supporting roller 41 as a rotary shaft. When the detection roller 43 is displaced so as to approach the coil 33, an eddy current loss accompanying the high-frequency field from the coil 33 becomes large, so that the amplitude of the high frequency signal from the oscillation circuit 35 becomes small.
On the other hand, when the detection roller 43 is displaced so as to be apart from the coil 33, the eddy current loss accompanying the high-frequency field from the coil 33 becomes small, so that the amplitude of the high-frequency signal from the oscillation circuit 35 becomes large. In such a manner, the distance between the detection roller 43 and the coil 33 is proportional to the amplitude of the high-frequency signal from the oscillation circuit 35. That is, since the distance between the detection roller 43 and the coil 33 is proportional to the thickness of the sheet P of paper, the amplitude of the high frequency signal from the oscillation circuit 35 is proportional to the thickness of the sheet P of paper.
The high frequency signal from the oscillation circuit 35 is detected by the detection circuit 38. Therefore, the direct current signal according to the amplitude of the high frequency signal is output from the detection circuit 38 to the amplifying circuit 39. The direct current signal is amplified by the amplifying circuit 39. An output signal of the amplifying circuit 39 is a signal corresponding to the thickness of the sheet P of paper.
FIG. 9 is a side view showing the configuration of a conventional thickness detecting apparatus 50. The thickness detecting apparatus 50 shown in the diagram is another configuration as an example and is disposed above the carrying path M. In the thickness detecting apparatus 50, a casing 51 houses the components. Aboard 52 is attached to an attachment bases 51b and 51c of the casing 51. A bobbin 53 is attached to the back side of the board 52 so as to be projected toward the carrying path M from the back side of the board 52. A coil 54 is wound around the bobbin 53. The coil 54 is to generate a high-frequency field in a manner similar to the coil 33 shown in FIG. 8.
A thickness detecting circuit 55 is attached to the surface of the board 52, and is obtained by packaging the oscillation circuit 35, the resistor 36, the capacitor 37, the detection circuit 38, and the amplifying circuit 39 which are shown in FIG. 8. The thickness detecting circuit 55 is connected to the coil 54 via a not-illustrated cable in a manner similar to the thickness detecting circuit 34 (refer to FIG. 8).
A detection roller 58 is disposed below the bobbin 53 (coil 54) and near an opening 51a of the casing 51, and is rotatably supported by a supporting roller 56 via a shaft 58a and an arm 57. The detection roller 58 is a conductor. A part of the detection roller 58 is projected from the opening 51a toward the carrying path M side. The detection roller 58 is rotated in a state where it is in contact with the sheet P of paper and is displaced in the direction Z in accordance with the thickness of the sheet P of paper. That is, the detection roller 58 is a roller which detects the thickness of the sheet P of paper as a displacement amount.
In the configuration, when the oscillation circuit 35 (refer to FIG. 8) of the thickness detecting circuit 55 is driven, a high frequency signal is supplied from the oscillation circuit 35 to the coil 54 via the resistor 36, the capacitor 37, and the cable (not shown). Consequently, a high frequency current is passed to the coil 54 and a high-frequency field is generated around the coil 54.
When the sheet P of paper is carried in the direction X in such a state, the detection roller 58 is rotated in a state where it is in contact with the surface of the sheet P of paper and is displaced in the direction Z in accordance with the thickness t1 (or thickness t2) of the sheet P of paper by using the supporting roller 56 as a rotary shaft. As described with reference to FIG. 8, the amplitude of the high frequency signal from the oscillation circuit 35 changes according to the distance between the coil 54 and the detection roller 58, that is, the thickness of the sheet P of paper.
The high frequency signal from the oscillation circuit 35 is detected by the detection circuit 38 (refer to FIG. 8) of the thickness detecting circuit 55. Therefore, the direct current signal according to the amplitude of the high frequency signal is output from the detection circuit 38 to the amplifying circuit 39. The direct current signal is amplified by the amplifying circuit 39. An output signal of the amplifying circuit 39 is a signal corresponding to the thickness of the sheet P of paper.
As described above, in the conventional thickness detecting apparatus 10 (refer to FIG. 7(a)) and the thickness detecting apparatus 20 (refer to FIG. 7(b)), the potentiometers 16 and 27 including the mechanical structure part are used as sensors. It causes a problem of high cost and a large size of the apparatus by the amount corresponding the space in which the potentiometer 16 or 27 is disposed.
Since the conventional thickness detecting apparatus 30 (refer to FIG. 8) has a configuration such that the coil 33 and the thickness detecting circuit 34 are separately provided and connected via the cable 40, noise easily occurs in the cable 40 and, further, it is very difficult to keep the distributed constant in the cable 40 at a constant value.
Therefore, in the conventional thickness detecting apparatus 30, since the stability of the distributed constant exerts a direct influence on the accuracy of detection of the thickness of the sheet P of paper, a problem of low detection accuracy exists.
Further, in the conventional thickness detecting apparatus 50 (refer to FIG. 9), at the time of winding the coil 54 around the bobbin 53, uneven winding occurs. Consequently, it is very difficult to maintain the inductance of the coil to a constant value. In a manner similar to the case of the thickness detecting apparatus 30 (refer to FIG. 8), the distributed constant becomes unstable. The conventional thickness detecting apparatus 50 therefore has a problem such that the detection accuracy is low.
In addition, in the conventional thickness detecting apparatuses 30 and 50, due to the thickness of the coil 33 (refer to FIG. 8) and the bobbin 53 (coil 54) (refer to FIG. 9), there is a problem such that the size of the apparatus is naturally large.
It is an object of this invention to provide a low-cost, small-sized thickness, and accurate detecting apparatus.